The invention relates to power transmission belts having an engineered surface and more particularly, to power transmission belts having an engineered surface comprising a region having a nonwoven material and a friction reducing agent.
It is known in the art to make power transmission belts from elastomeric materials having an embedded tensile member. The belts may describe a multi-rib, toothed, v-belt, or flat profile. The belts run in pulleys having a matching profile.
It is known that the rib flank surfaces of V- and multi-v-rib belts are subject to sliding wear, temperature extremes, normal, tangential and frictional forces that cause belt noise, rib surface sloughing, slipping, and chatter. It is also known that power transmission capacity and belt longevity are functions of several factors, including the type of material contacting the pulley surfaces. These issues are conventionally addressed by incorporating a high loading of various fibers into the mix of the undercord materials that form the compressive layer of the belt. These fibers, or portions of them, are exposed when the V profile is cut or ground to form the belt from the cured belt slab. The resulting surface is a combination of the base polymer and exposed fibers. This technique is limited with regard to an engineering approach for composite design, and/or controlling friction, noise, and slippage. It also creates a stiff structure that resists bending, which can contribute to belt rib cracking and shortened belt life. Also, the addition of short fiber to the rubber under-cord material provides new flaw sites and stress risers from which cracks can initiate and propagate. Thus, the short fibers themselves can shorten the overall flex life of the belt. Representative of the art is U.S. Pat. No. 4,956,036 (1990) to Sedlacek which discloses a discontinuous fiber loaded compressive layer in a multi-v-ribbed belt. The belt is ground to create the required rib profile, thereby exposing the fibers. The elastomeric body portion is loaded with fiber preferably from about 0.5 to 20% by volume, with preferred loading at 3% by volume.
It is also known to address the above mentioned surface frictional problems by incorporating a friction modifying substance throughout the elastomeric body portion. Representative of the art is U.S. Pat. No. 5,284,456 to Connell et al. and U.S. Pat. No. 6,855,082 to Moncrief et al. This approach is limited by any adverse effects of the modifier on the physical properties of the belt body, and it results in wasteful use of modifier in non-surface regions and in ground-off portions of belt. In other art, a lubricant is coated, applied or treated onto the pulley contact surface of the belt. Representative of coating art is U.S. Pat. No. 5,851,635 to Di Giacomo et al., U.S. Pat. No. 6,004,238 to Hayashi et al., and U.S. Pat. No. 6,419,775 to Gibson et al. Coatings, applied in a thin layer to minimize dimensional impact to the profile, may not have sufficient durability. Coatings also require an additional manufacturing step.
It is also known to address the above mentioned problems by incorporating a nonwoven region on the rib flank surfaces. This permits the surface properties to be designed independently of the bulk of the belt structure. This technique is also limited. The nonwoven region may abrade and wear off, leaving exposed to the pulley a rib material which may have unsuitable friction and noise characteristics and reduced longevity. If the rib material must be designed for improved longevity, friction, and noise, for example by adding a friction reducing agent and/or fiber throughout, then the designer has not gained anything in design flexibility by having a separate nonwoven region. Representative of the art is U.S. Pat. No. 4,892,510 (1990) to Matsuoka which discloses a v-ribbed belt having a surface layer comprising a nonwoven fabric at the outer surface vulcanized to ribs solely made of rubber. The nonwoven fabric may be 0.1 to 0.3 mm thick and may contain a friction reducing agent.
Also representative of the art is U.S. Pat. No. 6,793,599 (2004) to Patterson et al. and U.S. Pat. No. 6,824,485 (2004) to Edwards et al. which disclose a v-ribbed belt having a nonwoven region on a pulley engaging surface, wherein the fiber-loaded elastomeric material of the belt body interpenetrates the nonwoven material. The fiber-loaded elastomeric material may also contain a friction-reducing or friction-modifying agent throughout the belt body and/or in the nonwoven region.
What is needed is a power transmission having a molded profile and an integrally molded, relatively thick, pulley-engaging region having a friction-modifying agent. What is needed is a power transmission belt having a nonwoven surface material on and commingled with a thicker, pulley-engaging region having a friction-modifying agent. What is needed is a power transmission belt with a multi-ribbed profile and having a nonwoven pulley-engaging surface layer and a compressive layer, with an in-between layer which interpenetrates the nonwoven layer and which has a friction-modifying agent to provide for longevity of low-noise performance. The present invention meets these needs.